When A. H. Worthen and his associates first studied the Pennsylvanian rocks of Illinois about 1870, they derived from the strata exposed in the valley of Spoon River in Fulton County a stratigraphic section that was used “for the coordination of the coal strata for the central and western parts of the State.” 2 Since then many detailed studies of local areas in this part of Illinois 3 have provided much additional information, but no generally accepted correlation. A systematic review of the Pennsylvanian stratigraphy was therefore begun by the writer, assisted by Mr. Sidney E. Ekblaw, in 1929 and continued in 1930 (figure 1).
Earlier investigators considered that the Pennsylvanian strata in western Illinois were marginal deposits in a sedimentary basin, the boundaries of which were nearly the same as those of the present Eastern Interior Coal Basin; that the higher strata overlapped to the margins of the . . .